In order to ensure that operators of electro-mechanical equipment are made aware of any faults which may arise in electronic components of the equipment, self-diagnostic systems are employed to monitor the components or sub-systems and to communicate a warning to the operator should a fault be detected. Such a warning may be in the form of a malfunction indication lamp (MIL) which is illuminated on a control panel.
In the vehicle industry, legislation now dictates that drivers of vehicles must be made aware of certain faults which may arise in the engine management system of the vehicle. For this purpose, self-diagnostic systems are employed to monitor the components or sub-systems in the engine management system and to communicate a warning to the driver should a fault be detected. Such a warning may be in the form of a malfunction indication lamp (MIL) which is illuminated on the vehicle dashboard. Depending on the severity of the fault, the driver may be instructed to visit a workshop immediately to have the fault rectified or, in the case of a minor fault, he may wait until the next scheduled visit to the workshop.
For certain engine management systems, primarily those which affect exhaust emissions, legislation dictates how frequently and under what circumstances diagnostic checks are to be performed. Accordingly, standard driving cycles exist during which all diagnostic checks must be completed. Legislation also requires that, should certain faults be detected during two consecutive driving cycles, these faults be permanently recorded in a memory so that they may be later accessed in the workshop.
Examples of engine management systems include an engine control module, an exhaust gas recirculation system, an evaporated fuel processing system, a secondary air system and a catalytic converter monitoring system. Further components which require monitoring may include an engine coolant temperature sensor, a mass air flow meter sensor, an engine speed sensor, etc. Whilst the functioning of some components can be checked virtually independently of the operating conditions of the engine, many components and systems can only be checked when certain operating parameters prevail, e.g engine load, temperature, engine speed, etc.
Accordingly, diagnostic systems have been developed which prioritize certain diagnostic checks over others. For example, a priority system is described in U.S. Pat. No. 5,331,560 in which certain diagnostic checks can be interrupted if operating conditions dictate that a diagnostic check can be performed on an engine management system for which the necessary operating parameters only rarely occur. Once the existing diagnostic check has been interrupted, the prioritized check can then be performed.
Due to the interrelationship between many components and sub-systems making up the engine management system, if operating conditions are such that a diagnostic check may be performed on one component or sub-system, it is necessary to inhibit diagnostic checks on other components or sub-systems which may otherwise affect the validity of the result of the diagnostic check. For conventional diagnostic systems, this implies that if a component or sub-system is added or deleted, the diagnostic system must be reprogrammed to ensure that the diagnostic system is aware of the effect of the new/deleted component or sub-system on the remainder of the engine management system. Naturally, the same problem arises when it is desired to implement the same diagnostic system in a different vehicle model.
The above-mentioned interrelation between various components and sub-systems further implies that should a fault be detected in one component, the effect of the fault may be reflected during diagnostic checks performed on several components or sub-systems. It is therefore desirable that means be available to accurately determine where the root cause of a fault lies and that no false fault signals be recorded.
In order to assist the workshop or manufacturer in determining why a certain fault has arisen, it would be useful to be able to obtain information pertaining to the actual operating conditions of the vehicle from the time the fault arose up to the point when the fault was detected. This possibility has not been available up until now.